Research overturns oldest evidence of life on Earth

March 16, 2011
By Brendan M. Lynch

Photomicrograph of clast in rock showing features under discussion (arrows point to some of these) Credit: Julienne Emry

(PhysOrg.com) -- It appears that the supposed oldest examples of life on our planet -- 3.5 billion-year-old bacteria fossils found in Australian rock called Apex Chert -- are nothing more than tiny gaps in the rock that are packed with minerals.

The new findings by geologists at the University of Kansas show that microscopic structures many scientists had thought to be primeval oxygen-producing cyanobacteria really are lifeless bits of hematite. The reexamination of the Apex Chert was published recently in Nature Geoscience, a respected peer-reviewed journal.

We found no sign of any microfossil, said Alison Olcott Marshall, assistant professor of geology at KU. What we found were minerals that took the appearance of life. We went into this assuming these were microfossils  as was pretty well accepted in the scientific community. It was a good lesson in trusting your data over what youd been told you should find. At every step of the way, we would do an experiment expecting to find one result and find the complete opposite instead.

Opaque microstructure similar to previously described microfossils, as it has both an opaque outer wall and septa-like features, with large clear patches inside. Credit: Allison Olcott Marshall

The research began when Olcott Marshalls co-investigator Craig Marshall, assistant professor of geology at KU, collected new samples of the Apex Chert rock in Pilbara Craton, Western Australia.

I went to the outcrop and with a geological pick I proceeded to break into the rock, Craig Marshall said. These rocks are very difficult to sample, theyre not crumbly like limestone. Youve got to really put your shoulder into it. I sampled from the microfossil locality, but I also sampled at 10-meter intervals, tracing up the formation.

After shipping the heavy rocks back to Kansas, the researchers carved one portion of the sample rock into 300-micrometer samples, as had previous researchers. But they also created another set of much thinner sections  30-micrometer slices  that allowed for more light to pass through the rock. Then they peered at the samples through a traditional microscope.

We were able to see all sorts of details and textures that has been lost in those previous studies, said Alison Olcott Marshall.

Opaque microstructure similar to previously described microfossils, as it has large opaque patches separated by clear septate-like structures. Credit: Alison Olcott Marshall

Next, the scientists analyzed the Apex Chert samples with the most complex Renishaw Raman spectrometer dedicated to paleontology in the United States, housed at KUs Multidisciplinary Research Building.

We impinge laser light onto a sample, and that induces the molecules to vibrate, and it scatters off light at a different wavelength, said Craig Marshall. That frequency can be diagnostic for different minerals or different organic materials, and you can use that to identify the composition of a sample.

Where previous investigators had found carbon-like materials  a telltale sign of life  the KU scientists, joined by graduate student Julienne Emry, instead found hematite, a mineral consisting of iron and oxygen bonded together.

There were carbonaceous materials within the rock, but not actually associated with these microstructures that had been previously reported to be composed of carbonaceous materials, Craig Marshall said.

In general, the scientists contend that more painstaking testing should be performed on all microfossils before they can be conclusively identified.

Bacteria are basically little bags of goo, and theyre not easily fossilized, said Alison Olcott Marshall. The idea that you would have this tiny bacterium preserved for 3.5 billion years is not very likely to happen. The second problem is that they are morphologically so simple  theyre just circles and rods. There are lots of things in nature that make circles and rods.

The rigorous techniques used by KU researchers on the Apex Chert pseudomicrofossils someday could help determine with more certainty the presence of life on other planets.

This work has direct implications for looking for life on Mars, said Craig Marshall. If were having problems here with ancient Earth sediments and theres a huge debate, we want to try and be more stringent with our analytic techniques. We dont want a repeat of the announcement in 1996 that, Wow, we found life on Mars. I cant recall the timeframe of how many days or weeks until they said, Well, maybe we havent. If we tighten up our ways of looking for ancient biology, this is going to be very applicable for Mars, particularly the ExoMars European mission in 2018 that will take on board a Raman spectrometer.

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I am glad to see that researchers are not distracted by the fact that it would be cool to find cyanobacteria that old, and do a rigorous peer review of the available data.

Every advance we make in determining "yeah that looks like it used to be life" or "no, that's minerals and minerals alone" will be helpful in the coming years when we start getting more (useful, I hope) results back from various probes throughout the solar system.

Scientists have no fear like the fear of being called idiots by their fellow scientists, in print. I suppose that works for everyone. Given that, everyone is highly motivated to make sure that their research stands up to very careful scrutiny.

Say what you will, but let's note a few things: (1) the scientists erroneously ascribed life to minerals. Why? Probably because they were "looking for" early life; (2) This is nice that they're finally correcting their error, but isn't it a rather gross error, moving the date for the first form of life from 2 billion to 3.5 billion years ago? (3) Darwin just lost a lot of time for the explanation of bacterial life. This means that bacteria "just appeared". Alas, this isn't what materialists believe (N.B. Darwin was effectively a materialist at the end of his life, negating his reference to the 'Creator's" "one or several forms".)

@Lino235 point 3 of yours isn't necessarily true. All these results mean is that we have not _yet_ found evidence of life back further than about 2 billion years. Maybe it doesn't look like what we expect it to.

And this is why that NASA scientist's work regarding "alien life fossils" evidence is weak. Voids and extrusions can look organic in origin, particularly at small (cellular) scales.

It's that these filaments are individually defined that bothers me. I would suggest early life fossils should predominately be found caked together, as mobility (and hence individuality) is likely an evolutionary adaptation.

Yes, it is entirely possible that life in some form was present 3.5 billion years ago or even further. All this tells us is that either life may not have been in a form that easily fossilizes or the evidence it did leave behind has not been found yet. Right? Just because you haven't found it, doesn't mean it doesn't exist. You have to prove that it doesn't exist or else it does. (wink) ;)

This does not say that bacteria did not have the time to evolve. If it turns out that there was no life quite that far back, it just means bacteria evolved faster at one point than we expected. Punctuated equilibrium already shows that evolution does not happen at a steady rate but rather slows and accelerates. Essentially we may have a "Cambrian-like" explosion during this time.

I would've thought that they would've done some more tests other than pretty much just visual. Don't they send it to a mass spectrometer, im sure if it were life it would have elements that would be out of place in soil or rock.

Don't they send it to a mass spectrometer, I'm sure if it were life it would have elements that would be out of place in soil or rock.

Yes. First, the original "discovery" was over a decade ago, and the work here doesn't directly contradict that work. Second, not everyone agreed that the original findings were evidence of life. Here is a fairly nice survey from a few years ago. Note that the marker that most reliably points to life is the C13/C12 ratio--which is determined by a mass spectrometer. (All C14 should be long gone.)

Anyway, if you follow the research above, and combine it with the prior research, it appears that by taking much thinner rock slices (0.000012 inches for those not metrically inclined) that they found that the carbon was not from the inclusions, but other parts of the sample underneath the "distinctive" markings.

This is probably not the end of the story either. The C13 ratio still has to be explained.

malamucika13

Mar 17, 2011

This comment has been removed by a moderator.

malamucika13

Early forms of life would not have developed hard shells or skeletons. These were later evolutionary developments.Thus should such a possibly more gelatinous life form have developed and died it would eventually have decomposed leaving nothing other than the space it had previously occupied. If events do not crush that space, then the space will eventually be filled by other deposits seeping through the rock. We find this with dinosaur fossils. The bone has long since gone, what remains is a mineralised substance that occupies the space previously occupied by the original bone.Perhaps there is a need to look a little harder to see if there is any evidence of structure, that could suggest that it is or could be the remnant of a living organism.